The prevent invention relates to a plastic lens and a method of manufacturing the same. More particularly, the invention relates to a technique to prevent a hard coat film from attaching to a fitting part of a plastic lens to be fit to a lamp body in a vehicle light assembly.
A plastic lens is superior to a glass lens in that its weight is light, its impact resistance is high and hard to be damaged, a freedom of configuration of design, a sharp lens cut formation is easy, and hence, a light distribution performance is improved, and so on. The plastic lens having such advantages are suitable for the lens of the vehicle light or lamp which must be light in weight, high in impact resistance, and is required to control light distribution.
The plastic lens is disadvantageous in that the wear resistance properties are poor, the weathering resistance is poor and solvent resistance is poor. Poor wear resistance leads to easy damaging of the lens, poor weathering resistance leads to deterioration of the lens by sun rays, and poor solvent resistance leads to easy cracking of the lens by the solvent attaching to the lens.
To overcome those disadvantages of the plastic lens, a hard coat film, which absorbs ultraviolet rays, is formed on the surface of the plastic lens.
An example of a vehicle light assembly having the plastic lens with the hard coat Elm is shown in FIG. 4.
A lamp body b includes a concavity c opened to the front. A bulb d is supported by the central part of the rear wall of the lamp body. A mounting edge e projected outward is formed on and along the edge of the opening of the lamp body b. A mounting groove f, opened to the front, is formed on and along the mounting edge e.
A front lens g consists of a front portion h dimensioned so as to cover the front opening of the lamp body b and a side portion i protruding substantially rearwardly of the circumferential edge of the front portion h. A rear end j of the side portion i of the front lens g serves as a fitting part. A substrate k of the front lens g is made of transparent synthetic resin, e.g., polycabonate, methacrylate, or the like. A hard coat film l containing ultraviolet rays absorbent is formed over the outer surface of the substrate k except the fitting part j.
The front lens g is mounted on the lamp body b in a manner that the fitting part j is fit into the mounting groove f of the lamp body b with sealing material m, e.g., hot melt, intervening therebetween.
The hard coat film l is formed over the plastic lens in the following manner. The outer surface of the lens substrate k of the lens is coated with resin composition of the ultraviolet rays curing type by, for example, a spray coating method or a dipping method. The resin composition coated on the lens substrate is exposed to ultraviolet rays to be cured into a hard coat film l.
If the hard coat film is adhered to the fitting part j, the bonding strength between the fitting part and the sealing material m is lowered.
The fitting part j of the lens substrate k is masked with a masking tool n as shown in FIG. 5. In this state, the lens substrate k is coated with the resin composition by a spray coating method or a dipping method. With the masking, the hard coat film l is not attached to the fitting part j. This method has the following disadvantages. It takes a number of film forming steps. If the masking tool n is poor in precision, the resin composition flows into the fitting part j through a gap between the lens substrate and the masking tool n. To avoid this, an expensive masking tool n must be used. If a high precision masking tool n is used, it frequently damages the fitting part j when the masking tool n is attached to the lens substrate. Furthermore, in this case, the resin composition frequently flows to the fitting part j when the masking tool n is removed after the coating process.
In the conventional plastic lens and the conventional method of forming a hard coat film on the surface thereof, the solvent evaporation performed before the resin composition is cured by ultraviolet rays is insufficient. Some amount of solvent is left in the resin composition. This residual solvent gives rise to fogging, blushing, and cracking of the hard coat film.